Government security forces are battling Muslim militants who have laid siege to a city in the volatile southern region of Mindanao.

These recent spate of attacks where terrorism plagued Marawi City in Lanao del Sur, have once again headlined the names of Abu Sayyaf’s Isnilon Hapilon and the Maute bothers in all local and foreign media – traditional outlets and in different online news organizations as well as social networking sites.

The magnitude and gravity of atrocities compelled President Rodrigo Duterte to declare martial law and the suspension of the writ of habeas corpus over Mindanao on Tuesday, May 23.

This upheaval in Marawi came about as the military launched a surgical strike in barangay Basak Malutlut against “high value targets” belonging to the Abu Sayyaf Group and the Maute Group.

An Arabic-speaking preacher with an engineering degree from the Philippines’ top university, Isnilon Hapilon, 51, is one of the world’s most wanted terrorists.

Hapilon was purportedly designated leader of the Islamic State group’s Southeast Asia branch last year but has long ties to local extremist movements.

Born in 1966, he was once commander of the Moro National Liberation Front, an Islamic separatist group.

He later ascended the ranks of Abu Sayyaf to become its second in command.

Abu Sayyaf, a notoriously violent Muslim militant group founded in the 1990s, is known for carrying out kidnappings and beheadings of Filipinos and foreigners, as well as bombings, assassinations and armed attacks.

Hapilon gained notoriety beyond the Philippines when he allegedly helped Abu Sayyaf kidnap 20 hostages from a Filipino resort in 2001. The victims included three U.S. citizens, one of whom eventually was beheaded.

In 2002, the U.S. Department of Justice indicted Hapilon over the attack. He is included in the department’s “Most Wanted Terrorists” list, with a $5 million reward for information leading to his capture.

In 2014, Hapilon appeared in a video beside two masked men pledging allegiance to the Islamic State group, which was then gaining ground in Iraq and Syria.

He went on to organize an alliance in the Philippines called Dawlatul Islam Wilayatul Mashriq, which is now believed to include at least 10 small militant groups including some Abu Sayyaf factions.

The Philippine military has targeted Hapilon repeatedly with large-scale military operations, and has come close to killing him.

But the militant leader remains elusive. In 2008, troops bombarded an Abu Sayyaf camp near Jolo island with artillery and mortar fire, reportedly wounding Hapilon in the hand.

He was also reportedly wounded in another operation in 2013. The latest close call came in January, when the military attacked militants with ground troops and airstrikes, dropping 500-pound (225-kilogram) bombs from military jets.

The operation left 15 militants dead, and the army said Hapilon was seriously wounded in the arm. Losing blood, he was placed on a makeshift stretcher, escaping into a mountainous region of Butig in southern Lanao del Sur province.